In known sampling devices, the high dust content of the samples gases (on average 100 g/m.sup.3) causes frequent blocking of the sampling conduits and the filters.
In addition, the need to ensure a short response time has led to the installation of the devices for sampling and analysing the gases as close as possible to the sampling locations. These devices have consequently frequently been exposed to high temperatures, very dusty atmospheres, and in some cases to corrosive discharges.
These conditions are extremely detrimental, not only to the apparatus, which must be frequently serviced and unblocked, but also to the personnel carrying out these operations. Consequently, known systems only have a very limited reliability in the difficult conditions described above.